Various types of actuators and brakes are known. For instance, a DC motor can be used as an actuator to control output torque. Such motors can be difficult to control for certain applications and may be large and heavy. Increasing the output torque generally requires increasing the size of the motor. DC motors are not ideal in many cases for providing resistive control or braking for these and other reasons. As another example, a friction brake can be used for resistive control but not for providing an output torque. It is disadvantageous in that it generates heat, is subject to wear and reliability problems, and can be harmed by contaminates. Magnetic brakes are known and used for resistive control, but not for providing an output torque. They also generate heat and can be hard to control and provide a “jerky” engagement. The MRF brake similarly is not useful for providing an output torque. It is also subject to excessive heat generation and can be heavy and large. Thus, these known types of actuators can either control output torque or modulate input torque, but none of them can perform both functions.
Rehabilitation of injured joints, such as the knee or elbow, can employ various approaches. In one approach, a passive orthotic device or orthosis is worn externally by an individual to provide constant support or resistance to the joint. In passive orthotic devices, the corrective or bias forces they supply are either constant or not capable of being changed in real time. These orthotic devices are widespread, and their relatively low cost, availability and simplicity have contributed to their usefulness.
Another category of rehabilitative device is able to change the resistance or applied force in real time, usually through some form of electronic control. Some of these devices are wearable and can be described as active orthotic devices. For example, one such device is able to lock the knee's position to avoid hyperextension and limit the range of motion. Another device is able to enhance or assist in mobility via the use of actuators. Generally, these devices are limited to retraining the natural gait motion and to muscle enhancement. These devices tend to be bulky and cumbersome, which hinders their use, and the inclusion of active elements increases the overall size, cost and weight.
The most effective tools for rehabilitation are rehabilitation machines, such as isokinetic and CPM machines. These machines are generally found in physical therapy, athletic training, or research facilities. They provide high resistive and sometimes assistive forces, while providing a unique tailoring of the rehabilitation regime to nearly any individual. Their broad abilities increase their proficiency as a rehabilitation tool.